Iridium and gold ?

[chignecto]

Hi , I am a rock hound,found a rock around five years ago,in nova scotia .I decide to look at it a year and a half ago , I broke a little piece off and it was all metal ,very heavy for the size ,very shiny. I was interested so I brought it to a business in Toronto who only sells gold by the oz. They used a xrf analyzer and they checked three times and the results were the same , it read 38% iridium , 4% au , 57% fe .The guy even had a senior member come over and she was shocked also,they did the test again , same result. I then had it tested by another xrf analyzer with similar result. Then one more and this one said it was mainly iron ,copper ,and ag . I didn't know what to think , so did some research , high amounts off iridium all lead me to a meteor. I then contacted a university professor at unb who is a expert , he did a rayman spec test and he said he identified the mineral jamesonite , which was mined in cornwall uk ,probally brought over as a ballast in ships . he said it was from there , then after asking him several times if there was iridium , he said there was none and no gold.
So I am very curious why the two xrf analyzer would say one thing and the rayman spec said another . Any help would be appreciated , can the xrf read incorrect ?

 

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[A2coins]

Thats weird find someone more reliable

 

[paleomaxx]

Handheld XRF analyzers can be really hit or miss. The signal produced is only from the surface of the sample being analyzed and as a result oxidation or surface contaminants can change the reading significantly from spot to spot. Sanding away the surface and then trying again can improve the quality of the readout but most handheld XRF units are designed for relatively homogeneous samples like metal alloys. Mineral composition can vary significantly between different grains in the sample rock and some minerals can have different proportions of certain elements and still be considered the same.

Raman spectroscopy can be used for mineral identification but since it looks at molecule bonds as opposed to elemental proportions and would not give useful data for a mineral that's mostly metal (like native iridium/gold) since metals would not show a polarization change.

For mineral analysis we used a mass spectrometer hooked up to a laser ablation apparatus. We could select a specific grain, vaporize it with the laser, and the the resulting gas was sucked into the mass-spec for elemental analysis. If we wanted information on the crystal structure as well as the elemental composition we would use x-ray diffraction which would give further clues as to the specific mineral. If it's a large geology department they might also have an EDS (energy dispersive x-ray spectrometer) which would give some very solid results. It might be hard to convince them to use any of those methods since they're fairy involved, but those are the surefire tools for elemental analysis.

 

[Tony in SC]

That's weird, iridium rare. Usually found in a thin layer.

 

[chignecto]

Thank You for the info , I really appreciate it .Are you familiar with the results of Raman spec , would it help if I showed you pics of the results they sent me ? I am going to contact the university again and see if it is possible to get a mass spectrometer or the EDS test done.This will be a long road.

 

[Tpmetal]

only way to truly know the content of anything is a good mass spectrometer